OREANDA-NEWS. Fitch Ratings has affirmed five classes from three U.S. Alt-A residential mortgage backed security (RMBS) transactions.

A summary of the mortgage pool and bond analysis can be found by performing a title search for 'RMBS Loss Metrics.' A spreadsheet detailing the actions can be found on Fitch's website by performing a title search for 'U.S RMBS Alt A Rating Actions for April 8, 2015' or by using the link.

KEY RATING DRIVERS

The three transactions included in this review were previously analyzed during an Alt-A sector review that took place in December 2014. During that review, the five classes above were excluded in error. Fitch is only taking action on the above classes and not all of the classes in the transactions due to the minimal difference in performance since December.

The five classes being affirmed are all Principal Only (PO) classes. Fitch's methodology for maintaining ratings on PO classes caps the PO rating at the highest rated senior and floors it at the lowest rated senior. The affirmations are driven by the stable performance of the underlying mortgage pool since the last review and the minimal rating volatility of the senior classes.

As a whole, ratings within the sector have been stable as more than 95% of classes were affirmed at their current rating during the sector review in December 2014.

RATING SENSITIVITIES

A detailed list of Fitch's updated probability of default, loss severity, and expected loss can be found by performing a title search for 'RMBS Loss Metrics' at 'www.fitchratings.com'. The report provides a summary of base-case and stressed scenario projections.

Fitch's analysis includes rating stress scenarios from 'CCCsf' to 'AAAsf'. The 'CCCsf' scenario is intended to be the most-likely base-case scenario. Rating scenarios above 'CCCsf' are increasingly more stressful and less-likely to occur. Although many variables are adjusted in the stress scenarios, the primary driver of the loss scenarios is the home price forecast assumption. In the 'Bsf' scenario, Fitch assumes home prices decline 10% below their long-term sustainable level. The home price decline assumption is increased by 5% at each higher rating category up to a 35% decline in the 'AAAsf' scenario.

In addition to increasing mortgage pool losses at each rating category to reflect increasingly stressful economic scenarios, Fitch analyzes various loss-timing, prepayment, loan modification, servicer advancing, and interest rate scenarios as part of the cash flow analysis. Each class is analyzed with 43 different combinations of loss, prepayment and interest rate projections.

Classes currently rated below 'Bsf' are at-risk to default at some point in the future. As default becomes more imminent, bonds currently rated 'CCCsf' and 'CCsf' will migrate towards 'Csf' and eventually 'Dsf'.

The ratings of bonds currently rated 'Bsf' or higher will be sensitive to future mortgage borrower behavior, which historically has been strongly correlated with home price movements. The ratings of outstanding classes may be subject to revision to the extent actual home price and mortgage performance trends differ from those currently projected by Fitch.